1. Field of the Invention
This invention is directed to an apparatus and method for scanning an object for an element of interest and especially for nitrogen in nitrogen-based explosives. More particularly, the invention is directed to an apparatus utilizing gamma-gamma resonance which causes gamma rays to be scattered by the element of interest that is detected and analyzed to provide a representation of the concentration of the element of interest contained within the object.
The subject apparatus and method finds further application in drug detection, body composition, industrial applications, substance detection, food analysis and medical applications including veterinary medicine.
This invention is further directed to a gamma ray detector utilizing a nuclear resonance fluorescence filtering element.
2. Description of the Prior Art
The technique of nuclear resonance fluorescence has been employed for elemental and isotope analysis, both qualitative and quantitative. Particular applications include devices for well logging, borehole prospecting, on-stream analysis and the analysis of planet surfaces.
A significant threat to human life and property exists when an explosive device is concealed in luggage or parcels brought into buildings, aircraft, etc. As a result, there is a need by both the public and private sector of the country for a reliable technique for the detection of such explosive devices. As the threat of terrorist activities throughout the world, especially in airports, has increased, the demand for an efficient and practical device for scanning luggage to determine the presence of explosives has intensified.
It is well known that explosives may be detected by sensing the amount of nitrogen in the object being examined. One technique of detecting nitrogen is by the subject method of nuclear resonance fluorescence (nuclear resonance scattering).
U.S. Pat. No. 3,171,961 relates to a method of well logging by nuclear resonance fluorescence for the detection of a given nucleus, particularly carbon and oxygen. Nuclear reactions are described as a method of providing radiation wherein a bombarding nucleon from an accelerator is employed to produce an excited nucleus of the atoms being detected in a geological setting.
U.S. Pat. No. 2,726,838 relates to the use of the reaction between accelerated elementary charged particles and target means to provide a monoenergetic neutron source for bombarding the analyzed object, thereby inducing a radioactive response which is detected. The preferred reaction is the reaction of deuterons with tritium.
U.S. Pat. No. 3,780,294 relates to the use of nuclear fluorescence for elemental analysis. The use of an accelerator to provide bombarding particles for nuclear reactions to produce gamma rays is discussed wherein the inventor indicates that the Doppler broadening may be too great and, therefore, would not provide a good method for the production of gamma rays.